In all my history of interviewing people, I've always found there's almost no info to be had in correct answers to any kind of question. You learn about a candidate once you guide them into territory where the fail.
Both where that line is, and how they handle the failure tells you a lot.
(Caveat: Make sure you're keeping it on the fail/no-fail edge, and you treat the candidate with respect. The point is not to show them that they're wrong, but to explore the boundaries of their skill set. Without being mean is a major goal here)
And if you can't push the candidate there: HIRE THEM. Right away. If they know that much more than you do that you can't get them beyond their limits, they are a fantastic addition to your team. (Provided they match personality-wise, too)
I've done the same - keeping on pushing until the candidate is on uncertain ground. (I interview for consulting/ analytic /business/ senior management roles.)
As most of a job is about doing things that haven't been done before, getting the candidate into unknown territory is when you really find out how effective they will be. Some people just stop, others switch seamlessly into problem solving mode and come up with an answer that may or may not work, and also with a plan to test whether it does.
One of my favorite interviews was like this. The interviewer started by asking me some of the basic logic problems. I had heard most of these many years before. He actually appreciated it when I stopped him mid-question and finished the question for him. He asked another one, I finished the question for him. He saw that I had a math degree and asked about a particular problem involving infinity that he had heard about, and I gave him the summary of a half-hour talk I had given on the topic. Finally he sat down and he told me about a startup he had worked on when he was young and we talked through the technical problems. He stumped me most of the time but we both agreed that it was a very enjoyable interview. Funny thing is, that was also the only interview I had ever been on where I didn't get the job. Probably because I didn't where a tie to the interview and this particular company is apparently known for requiring ties.
That's why I always asked for dress code before the interview. You may feel slightly stupid when you ask, but you'll be dressed right when you come to the interview.
This sounds like a great technique. It also gives both sides the chance to talk a problem through, bounce ideas off of one another, and see if there are any interesting insights to be had on the other side of the table.
A candidate and interviewer both have to be fairly relaxed and comfortable to do it properly, but that's more of a problem for people new to the interviewing process (probably not senior management roles)
It also gives both sides the chance to talk a problem through, bounce ideas off of one another, and see if there are any interesting insights to be had on the other side of the table.
Some companies do this intentionally without hiring anybody in order to double-check their plans. It's basically free consulting.
That can be gamed as well. The OP could have let himself be pushed further by getting it done faster, but he did the "silly but adorable" thing of solving it with some mumbling and hesitation, which seemed to convince the interviewer they had seen his learning process. Someone more devious — betting on an unusual interview style — might have failed some answers on purpose.
Both where that line is, and how they handle the failure tells you a lot.
(Caveat: Make sure you're keeping it on the fail/no-fail edge, and you treat the candidate with respect. The point is not to show them that they're wrong, but to explore the boundaries of their skill set. Without being mean is a major goal here)
And if you can't push the candidate there: HIRE THEM. Right away. If they know that much more than you do that you can't get them beyond their limits, they are a fantastic addition to your team. (Provided they match personality-wise, too)